Unable to capture wlan traffic from other wireless clients

Sorry, this is maybe a recurring topic but I still don't see clearly the reason why I can't sniff the traffic from other wireless clients connected to my access point. My host machine is running under ubuntu 14.04, with a wireshark version 1.10.6 and a wireless NIC "Intel Corporation Wireless 7260 (rev 83)"

I used airmon-ng to create an interface in monitor mode (mon0) in the operating channel.

sudo airmon-ng start wlan0 6

In practice, I stay associated to the AP but I can only sniff my own traffic. I read that this could be due to the half duplex communication which could prevent to capture all the packets. So I tried to disable the WiFi in the Network manager to put my card in a pure sniffing mode but then I don't capture anything. Note that before starting the capture while WiFi is diabled, I used the following commands to set up the wlan interface:

sudo rfkill wlan0 unblock wifi

sudo ifconfig wlan0 up

sudo ifconfig mon0 up

I also tried airodump-ng to remove any doubt regarding the wireshark configuration (e.g Promiscuous mode) and again no packets from other clients...

Is the monitor mode of my wireless card very specific and prevents to capture the traffic from other wireless clients? How to make sure that this is a limitation from my wireless card? Note that I gave a try with the Linux Mint 17 distribution but it didn't help.

I heard about the special USB capture adapter ("AirPCAP") but I though that it was particularly required under windows but not linux. Should I use this kind of adapter or is there something wrong or missing in my configuration setup?

Thank you for any feedback.